Did you make any other change to your services recently? It is possible there could be a 'stuck' order in the system keeping you from making any other changes, including adding channels, until it clears out. Tech support would need to create a support ticket to have the issue fixed. Had it happen once and it took several weeks to rectify.
If that isn't the issue you'll need to keep trying support until someone is able to find the issue.
Good luck!